The present invention relates to joint prostheses, and more specifically to a hip joint prosthesis configured for being anchored in a femur, however other joint implants are contemplated as being suitable with the present invention.
Hip prostheses, also referred to as hip joint implants, are known having a blade-like shaft or stem which is anchored in a patient's femur. A ball is fitted to an upper end of the shaft and is disposed at an angle relative to a longitudinal axis of the shaft to simulate the upper end of the natural femur. In some cases, the shaft is anchored in the femur in a cement-free manner by jamming and/or wedging the shaft into the cortex of a surgically prepared femur. This jamming takes place primarily in the area of the diaphysis, that is, in the distal part of the shaft and requires that the surgically hollowed space and the shaft form and size be carefully matched and adjusted relative to each other. Alternately, some shafts are held in the femur with cement.
During initial installation of the hip implant, it is important to properly align the implant relative to the femur, so that the ball end does not easily become disengaged during the patient's normal range of motion. An artificial hip joint can dislocate if the ball disengages from the socket. There is greater risk just after surgery, before the tissues have healed around the new joint. A hip that dislocates more than once may have to be revised to make it more stable. This requires supplemental surgery.
In some cases, it may also be necessary to remove and re-insert the shaft several times during a surgical procedure. For this reason, the shafts have been provided with a bore in the roof-ridge shaped proximal end which is perpendicular to the sides of the blade to permit the use of a hook-shaped instrument for pulling or driving out the shaft from the femur.
Often, conventional hip joint implants wear out and require surgical intervention to make repairs or to replace worn components. To facilitate the presurgical ordering of spare components, conventional hip joint implants are often provided with a plurality of holes or bores in a manufacturer or designer-specific pattern, so that the particular brand of implant can be recognized on X-rays. The holes are specifically designed to facilitate identification of the implant under X-ray. In many cases, the number, alignment and relative positioning of adjacent bores on the blade are indicative of a particular implant manufacturer.
Regardless of the reason, the removal of an existing hip implant stem is a laborious process, since the patient's bone has usually grown around, and has become integral with the implant. Due to the problems and stress on the patient when an implant is removed, surgeons typically take great pains to obtain a correct initial alignment of the implant relative to the femur to reduce dislocations and subsequent adjustments or removal.
Thus, there is a need for a system to more accurately align hip implants in the femur.